1. Field of the Invention
The present invention relates in general to steering columns of wheeled motor vehicles, and more particularly to steering columns of a type wherein, like those used in an automatic driving system, a steering shaft thereof is powered by an electric motor. More specifically, the present invention is concerned with an arrangement through which a torque transmission from an electric motor to the steering shaft is assuredly made even if a relative displacement occurs therebetween.
2. Description of the Prior Art
Electric steering columns are used in the field of automatic driving system wherein operation of the steering shaft is carried out by an electronically controlled electric motor without manipulation by a driver. One of such steering columns comprises a worm wheel which is concentrically mounted on the steering shaft and a worm which is fixed to an output shaft of the electric motor and meshed with the worm wheel. The electric motor is held by a jacket tube which covers and extends along the steering shaft. Thus, upon energization of the electric motor, a torque of the electric motor is transmitted to the steering shaft through the worm and the worm wheel. The torque of the steering shaft is then transmitted to a steering gear box for controlling steered road wheels. Usually, the worm wheel is fixedly disposed on the steering shaft by means of spline connection or the like.
However, in the above-mentioned steering column, quite precise manufacturing work is needed for assembling the steering shaft and the jacket tube. That is, if such precise work is not provided, an ill-alignment tends to occur between the two members, which causes a poorly or incompletely meshed engagement between the worm and the worm wheel. Of course, in this case, the torque of the electric motor is not smoothly transmitted to the steering shaft due to increased friction caused by the poorly meshed engagement. Furthermore, the direct engagement between the worm and the worm wheel tends to produce noises.
It is therefore an object of the present invention to provide an electric steering column which is free of the above-mentioned drawbacks.
Another object of the present invention is to provide an electric steering column which can be easily assembled.
According to a first aspect of the present invention, there is provided an electric steering column which comprises a steering shaft; a jacket tube extending along the steering shaft to cover the same; a worm wheel rotatably held by the jacket tube, the worm wheel having a center bore through which a given portion of the steering shaft loosely passes; a collar member tightly disposed on the given portion of the steering shaft defining an annular clearance between the collar member and the worm wheel; an elastically deformable structure put and compressed in the annular clearance in such a manner as to induce a rotation of the collar member when the worm wheel is rotated; and an electric motor that rotates said worm wheel with an electric power.
According to a second aspect of the present invention, there is provided an electric steering column which comprises a steering shaft; a jacket tube extending along the steering shaft to cover the same; a housing fixed to the jacket tube; a worm wheel rotatably held in the housing, the worm wheel having a center bore through which a given portion of the steering shaft loosely passes; an internal gear structure integrally formed on a cylindrical wall of the center bore of the worm wheel; a collar member loosely received in the center bore of the worm wheel and tightly disposed on the given portion of the steering shaft; an external gear structure integrally formed on a cylindrical outer wall of the collar member, the external gear structure and the internal gear structure being meshed while leaving a certain space therebetween; O-rings made of elastic material, each O-ring being compressed between the internal and external gear structures to induce rotation of the collar member when the worm wheel is rotated; and an electric motor held by the housing, the motor rotates the worm wheel with an electric power.
According to a third aspect of the present invention, there is provided an electric steering column which comprises a steering shaft; a jacket tube extending along the steering shaft to cover the same; a housing fixed to the jacket tube; a worm wheel rotatably held in the housing, the worm wheel having a center bore through which a given portion of the steering shaft loosely passes; a collar member tightly disposed on the given portion of the steering shaft while defining a cylindrical space between the worm wheel and the collar member; a resilient collar unit disposed and compressed in the cylindrical space to induce rotation of the collar member when the worm wheel is rotated; and an electric motor held by the housing, the motor rotating the worm wheel with an electric power.